Interfacial and bulk spin Hall contributions to fieldlike spin-orbit torque generated by iridium

Abstract

We present measurements of spin-orbit torques (SOTs) generated by Ir as a function of film thickness in sputtered Ir/CoFeB and Ir/Co samples. We find that Ir provides a damping-like component of spin-orbit torque with a maximum spin torque conductivity 𝜎 𝐷𝐿 𝑒𝑓𝑓 =(1.4 ± 0.1) × 10 5 ℏ 2𝑒 Ω −1 𝑚 −1 and a maximum spin torque efficiency of ξDL = 0.042 ± 0.005, which is sufficient to drive switching in an 0.8 nm film of CoFeB with perpendicular magnetic anisotropy. We also observe a surprisingly large field-like spin-orbit torque (FLT). Measurements as a function of Ir thickness indicate a substantial contribution to the FLT from an interface mechanism, so that in the ultrathin limit there is a non-zero FLT with a maximum torque conductivity 𝜎 𝐹𝐿 𝑒𝑓𝑓 = −(5.0 ± 0.5) × 10 4 ℏ 2𝑒 Ω −1 𝑚 −1 . When the Ir film thickness becomes comparable to or greater than it's spin diffusion length, 1.6 ± 0.3 nm, there is also a smaller bulk contribution to the fieldlike torque.

Multiple modes of perpendicular magnetization switching scheme in single spin–orbit torque device

“…Strong field-like torque has been reported in previous researches. [20][21][22] Moreover, a number of researches have demonstrated that both the strength and sign of λ FL /λ DL can be adjusted by tuning the material types or fabrication processes. [20,23,24] The strength of field-like torque is related to multiple factors such as layer thickness, material system, interfacial intermixing, etc.…”

“…Recent researches have reported several methods of enhancing the field-like torque. [22,24] In this work λ FL /λ DL = 4 is chosen for a preliminary study. Accordingly, macrospin simulation results under the various current densities are shown in Fig.…”

Field-Free Magnetization Switching Induced by Bulk Spin–Orbit Torque in a (111)-Oriented CoPt Single Layer with In-Plane Remanent Magnetization

“…Spin–orbit torque (SOT)-driven magnetic switching has attracted a lot of attention because of its significant application potential in nonvolatile, low-power, high-speed, and high-density magnetic random access memories and emerging spin logic devices. − The bilayer structure consisted of strong spin–orbit coupling (SOC) materials (e.g., topological insulator, two-dimensional electron gas, and Weyl semimetal and heavy metal) and ferromagnetic (FM) materials is widely accepted as the basic strategy of SOT switching. − However, the thickness of the FM layer in the bilayer structure is subjected to the non-local spin injection and spin coherence length, and the critical current density ( J c ) is enlarged with the increasing thickness of the FM layer, that is, the interfacial nature of the SOT effect. This peculiarity results in incompatibility between low J c and a thick FM layer for high thermal stability, which hinders the application of SOT-based devices in low-power and high-density memory and computation systems. − …”

Large Interfacial Rashba Interaction Generating Strong Spin–Orbit Torques in Atomically Thin Metallic Heterostructures

“…In the pioneer experiments by Miron et al in Pt|Co|AlO x , SOT was discussed in terms of dominating FLT arising from REE at the Co|Oxide interface, larger than SHE-DLT from Pt, suggesting the crucial role of a large interfacial electric field at the ferromagnet/oxide interface. Although, in metals, SHE is largely considered as the primary source of DLT, ,− a significant interfacial REE has been recently observed in Ir|ferromagnetic|Ta contributing to DLT . In the limit of atomically thin magnetic layers, additional mechanisms might also influence the strength of the SOTs: spin-filtering or charge quantum confinement, − surface states of topological insulators (TIs) and 2D electron gases …”

“…In the case of thick ferromagnet, it is known that SOT from SHE is determined via the complex spin-mixing conductance. 21,42,43 For t Co than the dephasing length, the description is far more complex owing to the remaining outgoing spin-currents and additional electronic reflections. We developed numerical analyses gathering most of the ingredients discussed above based on generalized drift-precession-diffusion equations 20,44−46 able to express the profile of the vectorial spin-accumulation μ̂F.…”